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refactor(inference): extract reusable RemoteInferenceGenerator#1911

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refactor(inference): extract reusable RemoteInferenceGenerator#1911
dyurk-lila wants to merge 4 commits into
NovaSky-AI:mainfrom
dyurk-lila:upstream/r3-remote-inference-generator

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Note on the diff: This PR is part of a routed-expert-replay / sampler-support series and builds on the PRs below. GitHub can't show the intermediate branches here, so the diff is cumulative on top of main — the changes new to this PR sit on top of:

Reviewing in PR order (lowest number first) shows each incremental change cleanly.

Summary

Pure refactor (no functionality change) that extracts the single-request HTTP
generation path out of RemoteInferenceClient so it can be reused on its own:

  • Extract the raw-token generation path into a standalone
    RemoteInferenceGenerator and a RemoteGenerateResult dataclass.
  • Have RemoteInferenceClient own an internal RemoteInferenceGenerator and
    delegate session management, _post, and _generate_single to it.
  • Expose optional routed-expert results without requiring callers to construct
    the full inference/control-plane client.
  • Preserve existing endpoint routing, retry/backoff, cache_salt handling,
    serialization, and lifecycle behavior.

Testing

  • uv run --isolated --extra dev --extra fsdp pytest tests/backends/skyrl_train/inference_servers/test_remote_inference_client.py
    (58 passed)
  • ruff and black clean on the changed files.

dyurk-lila and others added 4 commits July 16, 2026 21:27
Fix routed-expert replay (R3) correctness for RL training and introduce a
shared token-metadata layout that later routed-expert and sampler-support
work builds on.

- Scope global RouterReplay state to one Megatron pipeline schedule so a
  forward-only logprob pass can no longer leak backward replay state into
  the next training schedule (clear before the schedule and in `finally`).
- Keep `rollout_expert_indices` ragged and treat its length as the
  captured-prefix length. Derive a `router_padding_mask` after left padding
  that marks alignment padding and the uncaptured trajectory suffix, and
  carry it through the training data, replay experiences, microbatch
  padding, and the Megatron model call.
- Build one `TokenMetadataLayout` per microbatch and apply it to both routes
  and the padding mask. Generic construction, alignment, next-token shifting,
  and packed-output restoration live in `skyrl/utils/token_metadata.py`.
- Pass Megatron's `padding_mask` through the model and apply a narrow
  compatibility shim so `[tokens]` masks broadcast over experts in expert-bias
  accounting.
- Slice every per-trajectory generator field generically during dynamic-sampling
  replacement and filtering so route metadata stays attached to its trajectory.

Synthetic padding rows use distinct dummy experts `[0, ..., topk - 1]`; the
mask excludes them from expert-bias accounting while preserving Megatron's
dropless `tokens * topk` dispatcher invariant.
Store routed-expert (R3) generation data as compact NumPy arrays instead
of large nested Python lists, and send it over the network base64-encoded
alongside its shape and dtype. Expert IDs are compacted to the smallest
safe uint8/int16/int32 dtype, vLLM responses and client responses use
orjson, and preprocessing accepts the decoded NumPy route arrays directly.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Under pipeline parallelism each rank replays only its local router
layers, but the Megatron worker eagerly expanded the full global-layer
routed-expert tensor to int32 before replay setup, allocating a large
device temporary for unused layers.

Keep routed-expert IDs in their compact dtype through whole-batch device
movement, index_select the current PP stage's router layers before
metadata alignment, and perform the single int32 conversion inside
_split_replay_indices so only the bounded PP-local slice is materialized
as int32. Also validate the 4D replay-indices shape up front.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Extract the single-request HTTP generation path out of
RemoteInferenceClient into a standalone RemoteInferenceGenerator and a
RemoteGenerateResult dataclass. RemoteInferenceClient now owns an
internal generator and delegates session management, _post, and
_generate_single to it.

This is a pure refactor with no functionality change: endpoint routing,
retry/backoff, cache_salt handling, serialization, and lifecycle
behavior are all preserved.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
@gemini-code-assist

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